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NSF PR 02-55 - June 26, 2002
Data Storage Gets Ultrasmall with Remarkable Breakthrough
in Electrical Resistance
Two materials researchers have developed an extremely
sensitive nanoscale device that could shrink ultra-high-density
storage devices to record sizes. The magnetic sensor,
made of nickel and only a few atoms in diameter, could
increase data storage capacity by a factor of a thousand
or more and could ultimately lead to supercomputing
devices as small as a wristwatch. The National Science
Foundation (NSF) supported the research.
As stored "bits" of data get smaller their magnetic
field gets weaker, making the bits harder to detect
and "read." Reliable reading of the data depends on
producing a large enough magnetically-induced change
in the electrical resistance of the sensor. Producing
a detectable change at room temperature is another
challenge.
In an experiment at the State University of New York
at Buffalo, Harsh Deep Chopra and Susan Hua demonstrated
that their tiny sensor produces an unusually large
change in resistance in an ultra-small magnetic field,
at room temperature. The magnitude of the magnetic
effect they created surpasses all previous records.
The results will be published in the July 1 issue
of Physical Review B.
The effect is based on spintronics, a rapidly growing
field that employs not only the charge but also the
spin of electrons in making electrical devices.
The current technology used in the heads, or sensors,
that read bits from a storage disk is based on an
effect called "giant" magnetoresistance (GMR). GMR
refers to the change in the sensor resistance when
placed in a magnetic field; the effect is typically
less than 100 percent. Inside a hard drive, a GMR
device senses the local magnetic field of a stored
bit of data. Such sensors have enabled commercial
hard drives that can store the amount of data contained
in a DVD full-length movie in a space the size of
a credit card.
The effect created with the new nickel device is called
"ballistic" magnetoresistance (BMR) and employs an
electrical conductor that is only a few atoms wide
and long. The BMR experiment exhibited a record change
in sensor resistance of more than 3,000 percent. Chopra
predicts the ultimate capacity will be about a terabit
per square inch. This could enable the storage of
50 or more DVDs on a hard drive the size of a credit
card.
Besides being useful for the multi-billion-dollar data
storage industry, the BMR techniques could improve
magnetic measurements and the study of magnetic effects
in individual atoms, molecules and nanoscale clusters.
It could also greatly enhance resolution and sensitivity
of scanning probe imaging techniques that are widely
used to characterize magnetic materials.
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